The present invention relates to a processing apparatus for and a processing method of executing a treatment including a process in which an object to be processed, such as a semiconductor wafer, is rotated so as to scatter liquid sticking on a surface of the object by centrifugal force due to its rotation.
For example, in the manufacturing process for a semiconductor device, various cleaning systems are employed for removing contamination, such as particles and organic contaminants, on the surface of the semiconductor wafer. Note, the semiconductor wafer will be referred as "the wafer", hereinafter. Above all, a cleaning system of the wet type where the water can be cleaned by dipping it into cleaning liquid in a processor has merit to remove the particles on the wafer effectively.
In order to permit a continuous batch process, the wet type cleaning system comprises a loader for loading, for example, twenty five wafers into the processing apparatus with every carrier, transporting means for transporting fifty wafers corresponding to two carriers loaded by the loader collectively, a processing unit arranged for cleaning and drying the wafers, which have been transported by the transporting means, in batch processing, and an unloader for unloading the wafers cleaned and dried. With these elements, this cleaning system is called "a wet station" in widespread use.
At respective processing sections constituting the wet station, a variety of chemical treatments, such as ammonia treatment, hydrogen fluoride treatment, sulfuric acid treatment, hydrochloric acid treatment etc., and a washing treatment with pure water are carried out by turns. Further, a drying treatment is executed finally.
As the processing section for drying the waters, there are well-known a rotary processing part in which the wafers are dried by shaking treatment-liquid off wafer surfaces due to the action of centrifugal force caused by rotating the wafers, and a IPA processing part in which the wafers are dried by draining while supplying water-amiable IPA [isopropyl alcohol: (CH.sub.3).sub.2 CHOH] steam to the wafer surfaces, conventionally. The rotary processing part which is also called "spin dryer" has the advantage of simple structure and low running costs because of disuse of an explosion-proof mechanism, in comparison with those of the IPA processing part. In the prior art, a spin dryer disclosed in e.g. Japanese Utility Model Publication (kokai) No. 5-83870 is well-known as the rotary processing (drying) part.
We now describe a structure of the conventional rotary drying part in brief. As shown in FIG. 1, a processing chamber 200 arranged in the rotary processing part includes a pair of rotating shafts 201, 202 arranged in serice. The rotating shaft 201 is one to which rotating force of a motor 203 is transmitted, while the other shaft 202 is a driven shaft. To the rotating shafts 201, 202, rotors 205, 206 in processing chamber 200 are attached respectively. A plurality of wafers W are collectively carried in their juxtaposed condition by constraint mechanisms 207, 208 bridging between the rotor 205 and the rotor 206. As shown in FIG. 2, the constraint mechanisms 207, 208 are provided, on surfaces thereof abutting on the wafers W, with numerous grooves 210 which are formed at constant intervals. In use, by inserting the peripheries of the wafers W into the groove 210, it is possible to carry the plural wafers W between the constraint mechanisms 207, 208 while keeping the wafers W to be juxtaposed apart from each other at regular intervals.
Further, against the processing chamber 200, not-shown intake port and exhaust port are connected for flowing air in the chamber 200. Since the wafers W are rotated while ventilating the chamber 200 through the intake and exhaust ports, it is possible to scatter moisture sticking on the wafers W by centrifugal force and also to dry the wafers W per se by the flowing of fresh air.
In such a rotary processing part, however, there is a case that the center or gravity of the wafers W and the center of rotation (of the rotating shafts 201, 202) do not overlap with each other. If the wafers W are rotated while leaving such a condition, vibrations may be caused during its rotation because of the ill-balanced rotary processing part. Therefore, from the points of view of the prevention of noise and the improvement in durability of the apparatus, it is necessary to adjust the balance of the rotary processing part so as not to increase vibrations caused by the rotation of the wafers W, thereby suppressing centrifugal whirling of the shafts. For this purpose, in the above processing part, two autobalancers 211, 212 are mounted on the rotating shafts 201, 202 rotating together with the wafers W respectively, for their integral rotation. In detail, the adjustment of balance is executed by moving counterweights accommodated in the autobalancers 211, 212 to appropriate positions.
It should be noted that the autobalancers 211, 212 have similar structures to each other. Therefore, we now describe the structure of autobalancer 211 mounted on the shaft 201 representatively. As shown in FIGS. 3A and 3B, the autobalancer 211 is provided with a pair of inside counterweights 213, 214. Since the counterweights 213, 214 rotate together with the shaft 201, centrifugal forces 215, 216 are applied on the counterweights 213, 214, respectively. In arrangement, the counterweights 213, 214 can be angularly moved freely within 360 degrees. In this regard, FIG. 3A shows a condition that the counterweight 213 is diametrically opposite to the counterweight 214 (at 180 degrees). In this case, a direction of centrifugal force 215 applied on the counterweight 213 is opposite to that of centrifugal force 216 applied on the counterweight 214, a resultant force of the centrifugal forces 215, 216 amounts to zero by their mutual negation.
While, FIG. 3B shows a condition that the counterweights 213, 214 are angularly moved from the positions of FIG. 3A by predetermined angles. In this case, the autobalancer 211 during rotation is subjected to a resultant force 217 consisting of the centrifugal force 215 applied on the counterweight 213 and the centrifugal force 216 applied on the counterweight 214. In this way, by optionally changing the positions of the counterweights 213, 214 in the autobalancers 211, 212, it is possible to change both direction and magnitude of the resultant force 217 consisting of the centrifugal force 215 applied on the counterweight 213 and the centrifugal force 216 applied on the counterweight 214. Thus, with the optional establishment in direction and magnitude of the resultant force 217, the balance of the wafers W rotating in the processing chamber 200 is adjusted in the conventional processing part. Note, as mentioned above, the autobalancer 212 has a structure similar to that of the autobalancer 211.
Now, as a method of seeking the most suitable positions of the counterweight 213, 214 in the autobalancer 211, 212 for adjusting the balance, the following method has been generally adopted conventionally. That is, in order to examine a relationship between the positions of the counterweights 213, 214 and vibratory values, it is executed at least once to rotate the wafers W and measure their vibrations while successively changing the positions of counterweights 213, 214 by e.g. five degrees (5.degree.) at a time on condition that the wafers W are accommodated in the processing chamber 200 of the rotary processing part previously. In this way, the most suitable positions of the counterweights 213, 214 to reduce the vibrations the most are determined on the basis of the obtained relationship.
However, it is impossible to seek the most suitable positions of the counterweights 213, 214 unless accommodating the wafers W in the processing chamber 200 and rotating them practically. Consequently, at least one superfluous rotating operation must be carried out before starting the rotation of the wafers W for dry, which is far from the shortening of processing period. Furthermore, according to the method, since the rotating operation of the wafers W has to be carried out despite that the balance is not adjusted yet, there is a problem that remarkable vibrations are produced during the rotating operation.
Recently, it has been found that the number of wafers W accommodated in the processing chamber 200 of the rotary processing part is closely related with the respective positions of the counterweights 213, 214. That is, to take an instance of the rotary processing part which is so constructed as to rotate the processing chamber 200 allowing e.g. a maximum of fifty sheets of wafers W to be accommodated collectively, there is a fact that when fifty wafers W are accommodated in the chamber 200, an operator has only to move the counterweights 213, 214 to prescribed angular positions. Similarly, the operator has only to move the counterweights 213, 214 to another prescribed angular positions in care of forty nine wafers W, while the operator has only to move the counterweights 213, 214 to the other prescribed angular positions in case of forty eight wafers W. That is, it has been found that, if the number of wafers W can be found out, the most suitable positions of the counterweights 213, 214 allowing their movement to be reduced to the maximum can be determined automatically. In this way, if only examining the relationship between the number of the wafers W and the positions of the counterweights 213, 214 previously, the operator has only to count the number of wafers W and sequent adjust the positions of the counterweights 213, 214 in accordance with such preset data, practically. Therefore, in such a case, there is no need for the operator to repeat the superfluous rotating operations every process.
Under such a circumstance, in the spin dryer disclosed in the above publication No. 5-83870, a counter consisting of a pair of light emitter and light receiver is provided in the rotary processing part for counting the number of wafers W accommodated therein and the adjustment for balance is carried out on the basis of the obtained discrete value. According to the method, the operator does not have to carry out the superfluous rotating operation before rotating the wafers for drying.
However, since the above spin dryer is adapted so as to begin to count the wafers for the balance adjustment after they have been accommodated in the rotary processing part, it is impossible to start to rotate the wafers as soon as they have been accommodated in the rotary processing part. For example, in the above-mentioned "wet" type of cleaning system, the wet wafers on which water is sticking due to the previous cleaning and sequent rinsing steps are to be accommodated in the rotary processing part. Accordingly, if such wet wafers are left as they are for a long time, the water will evaporate naturally, so that so-called "water marks" will appear on the surfaces of the wafers disadvantageously.
In addition, since the spin dryer in the above publication No. 5-83870 has the counter arranged in the rotary processing part, the water scattering by the rotation of the wafers may stick on the light emitter and the light receiver to cause their malfunctions. Furthermore, since it takes a long time from the dryer's accommodating the wafers in the rotary processing part till the starting, it is difficult to shorten the processing period. Additionally, since the rotary processing part of the spin dryer is not so wide in general, there are some cases of difficulty to arrange the counter in the rotary processing part.